Disclaimer: this is in NO WAY a jab or instigating thread to all those that have done a big bore build, but instead a question posed by a neophite that cannot sleep at night because of the inticing draw of going big on my motor, so please keep it clean and mature.

History: I have an '07 Ultra and at first I didn't want to have to split my cases to go big bore so a 107" is something that I'd always dreamt of. Well, now after talking to the mechs at work, splitting the cases doesn't seem like a bad idea and since my cylinders and all would be sitting on a work bench with a tear down already, might as well take the lower end out and have it re-worked RIGHT as well.

Question(s): If/since I would be splitting the cases anyways, I'd like to go up to 120cu. in, however, the conversation has been about the potential of losing reliability. Now the parts I'd use would compliment each other andnot some hodge-podge mix and match, they'd more than likely be HQ matched parts. 113" sounds nice too, but I'd really like to go 120" and be done with it, but the mere thought of losing reliability just because I'd have a large displacement is not something I'd want to partake of.

I ride my baby for long distances when we do ride and alot of time is spent out in the sticks in the middle of nowhere. I doubt I could trade the wifes'T-backs and bra space in the tourpak for a toolset for emergency teardowns, but stranger things have happened.

Thoughts about the loss(if any) of reliability and/or engine longevity by going to a BIG bore(120") would greatly be appreciated. Is this something you guys would do on your only bike, and one that you ride for "touring?". I need help...........mentally.[&o]

 

Big bores are just as reliable as stock bore motors . When you try and build one to get every ounce of hp out of it they start to be a little fickle . Whatcuts down longevity on a motor is the stroke (aka piston speed) . Try and stay under 4.5' stroke and you will be fine . Monster cams and high compression (over 11-1) will effect your longevity . Big bores put together for longevity will be as good as stock for that matter . I'm no good at it . All my motors are over 11-1 compression and run large cams . I don't have any problems . I run the hell out them but take very good care of them too . Go with a well known builder and let them know your intentions . They will match the motor to your riding style . I would do it in a hart beat !

 

I ride at least two touring trips a year, at least 3,000+ miles. I need the realibility also. I have had no concern in my BB kit when I went to the GMR 107". I am confident it will prove itself reliable.

 

With a "quality package" & and proper installation, you should actually increase (not decarease) reliability.

With a professional grade setup, you end up with very precise tollerances vs mass production tollerances. The older bikes get gear driven cams which remove the tensioner issue. All builds get the INA inner cam bearings replaced w/torringtons which
is an improvement.
In the scenario you gave, the Jims crank that would be used in the kit is far better than the crank you have now (that is known to have sissoring issues).

All that said, my bikes are. Built to ride - anywhere, anytime. I have ridden in all but a very small handful of US state + some in Canada. The only problems I've had on the road were flats, a loose compensator sprocket, & a failed starter clutch. Of those, only the starter clutch was motor related & it was not on an HQ motor. Based on that issue, it was a topic of conversation during my very first call to Doug. He assured me that if I followed his recipe, that would be a non-issue, and it has been just that.

For me.... I feel much better heading out on a 5k mile vacation ride with a motor I built than a new stocker.

 

I second Phil !

 

I'm glad you asked this, because I have been going through the same thing. I have a Stage 1 in my 07 EG and it runs really well. Now, just to clarify, when I say it runs really well, I mean that it runs good all day long with no oil usage, doesn't make any overly funky noises, starts every time, pulls 5000 rpm like a dream, is smooth, carries me solo fast enough to annoy all kinds of LEO's and carries me and the missus fast enough that I get the "warning tap" to the back of the head every now and then. So.....do I risk all of that to punch it out for for more juice? Don't get me wrong, more juice is always a good thing, but at what risk? When I am on the Oregon Coast, or riding the Grand Canyon, or some other location a long ways from home, I'm not sure I want to be concerned about whether or not my 100/100 motor is gonna get me home.

I know there are folks here who have built motors in their touring bikes and are having good luck with them, and I know that I will probably join those ranks eventually, but, with my luck....!? LOL!

My "go to guy" at the dealership and I have discussed this whole issue a number of times and he just laughs and says "around here, we like to say if it ain't broke, fix it till it is".

What to do, what to do?[sm=confused06.gif]

 

Phil, those are some very valid points......

 

UK
YOu know I am building a 120" and threfore may be a little biased, but will answer as intelligently as possible. I too rice long distance, and into the middle of nowhere at times. Last year went for 17 days, 4k miles and this was on a 103" build that was built to the max for HP and torque. Had absolutely no problems. Put 10k miles on the build and at the end was still not using a drop of oil and the bike was a joy to ride.
Going larger is not really a problem as long as you do not go "oer the top" with the build with hi-lift cams, compression beyond 10.5:1 and a tune that is trying to wring every last bit of hp and tq, reliability and redeability will not suffer. As an example, these big builds will get you 50+ mpg due to not having to use as much throttle to keep the bike in motion as a build with less power.
I would not go this route if I was at all concerned about reliability. I am not concerned at all. One thing, if you do go to 120" use a good crank, and have it the bottom end preffesionally done. Phil, myself, even Doug from HQ have sent ours out to have the bottom end beefed up a bit, all adding to the reliability of the engine. Hope this helps.

 

The build on my motor has 46,000 miles on it and no probs at all - 95" kit, 10.25:1, 211 cams... Still going strong.

 

What thye said ....

Do it